1. Field of the Invention
The present invention relates to the field of wireless communication systems and electronic processing and, in particular, transmission and reception architectures between a radio frequency (RF) receiver and transmitter. More specifically, but without limitation thereto, the present invention pertains to a communications system and method that allows mobile ground terminals, or smart antennas to, dynamically realign itself to the signal polarizations of a designated asset (primarily satellites) utilizing a cost optimization program, reuse frequencies via orthogonal polarization beams, and switch receiving polarizations between circular polarizations (CP) and linear polarizations (LP).
2. Description of Related Art
In wireless communications, satellite to ground terminal communication technologies are currently utilized in two different ways. Fixed Service Satellites (FSS) utilize satellites placed in geostationary orbit (GEO) transmitting and receiving signals from ground terminals that are fixed in position. Direct-to-Home (DTH) satellite dishes that serve to bring satellite-beamed television into private homes are an example of FSS. On the other hand, Mobile Service Satellites (MSS) rely on GEO satellites to transmit and receive signals to and from mobile terminals, such as a Global Positioning System (GPS) receiver in a car, boat, etc.
FSS and MSS are just two methods of wireless communications that utilize polarization diversity, each with differing applications and requirements. Polarization diversity has enabled the same frequency to be reused over the same spectra, allowing one frequency to transmit two or more distinct sets of information. This has proved to be beneficial to both RF communications and RF radar applications. RF transmissions are usually either circularly polarized (CP), or linearly polarized (LP). LP signals can be polarized either vertically (VP) or horizontally (HP). Additionally, CP signals can either be right-hand circularly polarized (RHCP) or left-hand circularly polarized (LHCP).
FSS systems typically employ a LP signals, as the ground receiver (terminal) is fixed, and there is no issue with the signals falling out of phase, interfering with each other, or unable to be received because the ground terminal does not move in relation to the satellite. On the other hand, due to the mobile nature of MSS platforms (such as a truck moving both directionally and spatially to the satellite), a CP signal offers a better option as it offers an omnidirectional radio wave signal that can be received and decoded regardless of the direction or spatial displacement of the terminal. However, there are some DBS (direct broadcast satellites) that utilize CP as well as LP signals.
Because of this, polarization alignment techniques are important on satellite communications to reduce interference due to misalignment of the orientations of transmission signals and received antennas either for large earth station antennas as well as the small aperture antennas found in VSAT (very small aperture terminals) and Direct-to-Home (DTH) services, such as those used for satellite-based television (e.g. DirecTV® or Dish® Network). Currently, the techniques used for polarization realignment are mechanical-based, using gimbals and tracks to physically rotate and re-orient the ground terminal to the satellite.
While mechanically driving the satellite receiver (also known as the ground terminal) is a practical method of re-orienting the dish to properly receive the RF signals, the gimbals and tracks pose a problem for mobile ground terminals. However, mobile ground terminals are limited in two important ways. The extra machinery necessary for mechanized terminal re-orientation adds unnecessary weight and complexity to these mobile terminals, when their chief aim is simplicity with low cost and weight. This is because these mobile terminals do not have the physical space or power requirements that the FSS systems have.
For the foregoing reasons, there is a need in satellite communications for a system to electronically re-orient, specifically but without limitation thereto, mobile ground terminal receivers to match the polarizations of satellite RF signals, thus removing the requirement of mechanically re-orienting the ground terminals. Furthermore, there is a need to create a system that allows mobile ground terminals to seamlessly switch between polarizations, allowing these mobile ground terminals to receive both circularly polarized RF signals as well as linearly polarized RF signals.
An embodiment of the present invention involves a dynamic improvement of how ground terminals receive RF signals from satellites by utilizing an electronic method of decoding transmitted RF signals from satellites, whether they are circularly polarized or linearly polarized. The proposed architecture will allow ground terminals, in particular mobile VSAT or DTV operators, to use satellite assets either with LP or CP satellites for their services. The ground terminals will dynamically realign itself via electronics, and not physically moving the receiver, to the polarizations of radiation from a targeted satellite.